1. Field of the Invention
The present invention relates to multilayer ceramic electronic components and in particular relates to the structure of an external electrode of a multilayer ceramic electronic component.
2. Description of the Related Art
In a power supply circuit of a circuit board on which a high-end LSI chip is mounted, if there are large fluctuations in voltage in a power supply line due to impedances that exist in the power supply line and the ground, the operation of a circuit that is being driven becomes unstable, interference occurs between circuits via the power supply circuit, and oscillations are generated.
Accordingly, typically, a decoupling capacitor is connected in parallel between the power supply line and the ground in order to solve this problem. Such a decoupling capacitor, together with eliminating parasitic noise in the power supply line, swiftly supplies charge to a load when fluctuations occur in the power supply voltage (quick power supply) and thereby stabilizes operation of the circuit. It is necessary to arrange an equivalent series inductance (ESL) low-value capacitor in the vicinity of the LSI chip to realize the above-described quick power supply, and for example, often an ESL low-value multilayer ceramic capacitor is arranged on the LSI package.
In line with the decreasing size and increasing capacitance of multilayer ceramic capacitors in recent years, there has been a tendency for internal electrodes of multilayer ceramic capacitors to be become increasingly thinner, for the number of stacked layers of internal electrodes to increase and for the ESL and equivalent series resistance (ESR) of multilayer ceramic capacitors to become lower. Consequently, for example, there has been a problem in that as a result of the ESR of a capacitor on an LSI package becoming too low, the impedance at a parallel resonance (anti-resonance) point generated between the capacitor and the very small capacitance of the LSI chip becomes high.
In other words, in a power supply circuit in which a plurality of decoupling capacitors, which have different electrostatic capacitances (intrinsic resonant frequencies), are connected in parallel with one another, if the ESR of a certain capacitor becomes too low, there is a problem in that the decoupling function in a certain frequency band will be degraded due to the influence of anti-resonance.
In response to this, for example, a way of increasing ESR by forming a resistance electrode layer, which is electrically connected to an internal electrode, in an external electrode serving as a terminal of a capacitor, has been proposed in PCT International Publications of Patent Application Nos. WO2006/022258 and WO2008/035727.
In the methods described in PCT International Publications of Patent Application Nos. WO2006/022258 and WO2008/035727, a resistance electrode layer is formed by applying a paste containing a resistive component to a ceramic body and forming an external electrode layer so as to cover the resistance electrode layer. In addition, such a resistance electrode layer is formed so as to wrap around from an end surface of the ceramic body onto adjacent side surfaces via corner portions.
However, when a resistance electrode layer wraps around onto a side surface, it is necessary that an external electrode layer wrap around onto the side surface by a greater amount in order to cover the resistance electrode layer. In this case, there has been a problem in that the distance from the edge of the wrapped around portion of the external electrode layer to the edge of the wrapped around portion of the resistance electrode layer becomes short and it becomes easy for moisture that has entered from between the edge of the wrapped around portion of the external electrode layer and the ceramic body to penetrate to the resistance electrode layer.
This kind of problem is encountered not only in capacitors that include resistance electrode layers as a measure to counter an increased ESR as described above, but also may be encountered in any multilayer ceramic electronic component in which an external electrode has a structure including two or more layers.